Zoom lenses of a five-group construction are known. For example, Japanese Laid-Open Patent Application 2000-292701, and Japanese Laid-Open Patent Application 2001-004919 disclose zoom lenses that include, in order from the enlarging side, a first lens group having negative refractive power and a focusing function and that is stationary during zooming, a second lens group having positive refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power, with the second, third, and fourth lens groups being movable for zooming, and a fifth lens group having positive refractive power that is fixed during zooming.
There has been a demand for a zoom lens of the type described in these Japanese published applications that provides a bright image even with a liquid crystal image source in a projection display device and that has the compactness desired in a projection display device. Additionally, it is desirable that the zoom lens be at least nearly telecentric on the reducing side and includes a large enough back focus distance to provide room for a color synthesizing optical system in a projection display device or, similarly, a color separation optical system when the zoom lens is used in a camera.
Furthermore, recently there has been a demand for projection to a large screen at a close distance by using a projection lens with an even wider field angle. For example, it is desirable to be able to project an image that is up to one hundred inches across with a projection distance of only 2.5 to three meters in projection display devices as described in the Japanese applications discussed above. Moreover, a larger zoom ratio has been desired in order to obtain this size image and to vary the size of the projected image.
However, with the increased use of projection display devices, the devices are not necessarily desirably placed directly between a screen and an audience, thus more freedom in placement is desired. For example, it may be desirable to hang the projection display device from the ceiling behind the audience and project an image over the heads of the people in the audience onto a screen. In this case, a zoom lens with a long focal length and that is telecentric on the reducing side is preferred for projecting the image, and when projecting to a one hundred inch image size as described above, a zoom lens designed for favorable optical performance with a projection distance of five to ten meters is required.